Solar ultraviolet B (UV-B) radiation (280-320 nm) has been associated with reduced risk of cancer of the breast, colon, ovary, and prostate, as well as non-Hodgkin's lymphoma (NHL) through the production of vitamin D in papers extending back to 1980. Using data on the geographic distribution of cancer mortality rates in the US, another ten cancers have been added to the list for which UV-B/vitamin D is a risk reduction factor (Grant 2002b; submitted). These associations persist even after additional cancer risk and risk reduction factors such as smoking, urban or rural residence, Hispanic heritage, poverty, dietary factors, and use of nonsteroidal anti-inflammatory drugs are added to the analysis. As a further test of the protective role of UV-B radiation, an ecologic study of cancer mortality rates in Europe with UV-B radiation and dietary factors was conducted. Inverse correlations are found for UV-B radiation for a number of cancers, with those for bladder, breast, endometrial, ovarian, prostate, and renal cancer, and multiple myeloma and NHL having the strongest correlations in this and ongoing multicountry ecologic studies. These studies add further support for the role of UV-B radiation and vitamin D in reducing the risk of a large number of cancers.